1. Field of the Invention
The present invention relates to an electrically controlled throttle apparatus for controlling an amount of intake air to be supplied to an internal combustion engine.
2. Description of Related Art
A conventional electrically controlled throttle apparatus comprises a throttle body forming an intake passage, a throttle valve for opening/closing the intake passage, a motor for driving the throttle valve, and a throttle sensor for detecting an actual opening degree of the throttle valve. The rotation of the motor is transmitted to the throttle valve through a speed reduction mechanism to thereby drive (open/close) the throttle valve.
To be more specific, the conventional electrically controlled throttle apparatus is arranged to detect the actual opening degree of the throttle valve by use of a throttle sensor, and drive the motor to control the opening/closing operation of the throttle valve so that the detected actual opening degree reaches a target opening degree. Some of the throttle sensors use hall elements. This type of throttle sensor is configured to detect the actual opening degree of the throttle valve by detecting changes in magnetic flux density caused by the opening/closing of the throttle valve (the rotation of a throttle shaft).
However, the electrically controlled throttle apparatuses, including the above mentioned one, which comprise the throttle sensor using the hall element sometimes could not control the amount of intake air with accuracy. This is because the throttle sensor tends to be influenced by a magnetic force leaking out of the motor and therefore cannot accurately detect the changes in magnetic flux density caused by the opening/closing of the throttle valve (the rotation of the throttle shaft). Hence, the output of the throttle sensor may change improperly. When the motor operates, furthermore, a current passing through the motor changes and thus the strength of the magnetic force that leaks out of the motor also changes, causing a further change in the output of the throttle sensor. As just described, the output of the throttle sensor is likely to change or vary under the influence of the magnetic force leaking out of the motor. As a result, the throttle sensor could not accurately detect the opening degree of the throttle valve. This makes it difficult to control the amount of intake air with accuracy.